Elastic and anelastic properties of C/Mg–2wt.%Si composite during thermal cycling

Ultrasonic technique is employed to detect microstructural changes induced in a carbon fiber–magnesium matrix composite (Mg–2wt.%Si alloy matrix reinforced by long unidirectional carbon fibers with volume fraction of about 30%) during thermal cycling in the range of 100–360 K through measurements of its elastic and anelastic properties. Variations of the elastic modulus of the composite during thermal cycling is largely determined by elasticity of the carbon fibers stressed by the thermally expanded/contracted matrix. Anelastic properties of the composite are caused by dislocation motion in the matrix.     

Monopulse Lasers Based on Yttrium Aluminum Garnet with Neodynium Ion with Resonators Based on an Optical Circuit of a Four-Pass Amplifier with Transverse Diode Pumping

The results of application in monopulse lasers based on yttrium aluminum garnet resonators with Nd³⁺ ions based on the optical scheme of a four-pass amplifier with one-sided lateral pumping of the active element by monospectral laser diode arrays are presented. The proposed resonator schemes make it possible to increase the output energy of single pulses of laser radiation. Monospectral gratings with efficient heat removal from laser diodes are capable of ensuring the operability of lasers with an increase in the repetition rate of monopulses and an expansion of the ambient temperature range.

     

A modified summation code for organizing control of combinatorial circuits

We propose a new modified summation code which has improved error detection characteristics as compared to the classical summation code. We define the properties of this code and propose methods to implement the generators of control bits.     

Summation codes for organization of control of combinational circuits

New modular and modified binary summation codes used for organization of the control of combinational circuits are considered. New properties are defined and the classification of codes is suggested.     

Laser emitters (λ = 808 nm) based on AlGaAs/GaAs heterostructures

AlGaAs/GaAs laser heterostructures with various active-region geometries, namely, with broadened asymmetric and narrow symmetric waveguides, and with various depths of quantum wells, are obtained by MOC hydride epitaxy. Single laser elements, bars, and arrays of laser diodes are fabricated from these samples, and their output characteristics are investigated. It is shown that the geometry of the narrow-waveguide structure is more preferable for laser-diode bars (λ = 808 nm). Increasing the charge-carrier barrier also favorably affects the output parameters of the bars in the case of heterostructures with a narrow symmetric waveguide, and the slope of the power-current (P-I) characteristics for these structures increases from 0.9 W/A to 1.05 W/A. The laser diode array of 5 × 5 mm, which is assembled based on the best heterostructure, shows an output power above 1500 W in the quasi-continuous mode at a pump current of 150 A.     

State and prospects of development of gradient calorimetry

The technology of heat flux measuring with the use of gradient-type sensors, which are based on natural anisotropic monocrystals and composites (heterogeneous media) containing layers of metals, alloys, and semiconductors, is described. It is found that the time constant of such sensors is from 10^?8 to 10^?9 s. The problems and prospects of using gradient calorimetry in thermal-engineering experiments and engineering practice are discussed.     

Self-Dual Self-Testing Multicycle Circuits: Their Properties

Functional testing of memory circuits based on the properties of self-dual functions and a procedure for transforming the initial circuit into a self-dual circuit are described. Experimental results for MCNC benchmark circuits are given.     

Gradient heat-flux sensors: Possibilities and prospects of use

Gradient-type heat-flux sensors (GHFSs) manufactured on the basis of anisotropic monocrystals of bismuth are proposed. These sensors can be used for measuring stationary and nonstationary heat flux as well as temperature, flowrate, and other parameters. It is shown that the multipurpose nature of the sensors makes it possible to considerably simplify experiments and increase their informational potentialities.     

Reduction of the grating lobes of annular arrays used in focusedultrasound surgery

An annular array with variable focus, used in focused ultrasound surgery, generates grating lobes responsible for undesirable lesions. It is known that the amplitude and the location of the lobes depend on both the geometry and the frequency of the transducer. A new procedure based on the use of a wide-band CW signal, i.e., a signal phase modulated by a pseudorandom code, is proposed to reduce the amplitude of these lobes. The theoretical study enables us to determine the location and the amplitude of these lobes and to simulate the effect of the transmitted signal bandwidth. In particular, a simple analytical relation gives the intensity ratio between the grating lobes and the main lobe. This equation shows that this ratio is inversely proportional to the number of rings and to the bandwidth of the transmitted signal. A system was developed and tested with two transducer arrays of 35- and 150-mm diameter, respectively. The simulations and experiments demonstrate the validity of the theoretical study and the efficacy of the proposed procedure. In conclusion, it is possible to reduce the grating lobes without geometric modification of the array by increasing the bandwidth of the transmitted signal     

Acoustooptic methods for measuring sound velocity

This paper gives a brief review of some studies of acoustooptic methods for measuring sound velocity in solids performed at the Department of Acoustoelectronics and Acoustooptics of the Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Science.